/*
 * (c) Copyright 2005, 2006, 2007, 2008, 2009 Hewlett-Packard Development Company, LP
 * All rights reserved.
 * [See end of file]
 */

package com.hp.hpl.jena.sparql.function.library;

//import org.apache.commons.logging.*;

import com.hp.hpl.jena.graph.Node;
import com.hp.hpl.jena.sparql.expr.ExprEvalException;
import com.hp.hpl.jena.sparql.expr.ExprException;
import com.hp.hpl.jena.sparql.expr.NodeValue;
import com.hp.hpl.jena.sparql.function.FunctionBase0;
import com.hp.hpl.jena.sparql.util.Symbol;
import com.hp.hpl.jena.sparql.util.Utils;

/** Function that returns the value of a system variable.
 *   
 * 
 * @author Andy Seaborne
 */

public class SystemVar extends FunctionBase0
{
    Symbol systemSymbol ;
    protected SystemVar(Symbol systemSymbol)
    {
        if ( systemSymbol == null )
            throw new ExprException("System symbol is null ptr") ;
        this.systemSymbol = systemSymbol ;
    }
    
    /** Processes evaluated args */
    @Override
    public NodeValue exec()
    {
        Object obj = getContext().get(systemSymbol) ;
        
        if ( obj == null )
            throw new ExprEvalException("null for system symbol: "+systemSymbol) ;
        if ( ! ( obj instanceof Node ) )
            throw new ExprEvalException("Not a Node: "+Utils.className(obj)) ;
        
        Node n = (Node)obj ;
//        if ( n == null )
//            throw new ExprEvalException("No value for system variable: "+systemSymbol) ;  
        // NodeValue.makeNode could have a cache.
        NodeValue nv = NodeValue.makeNode(n) ;
        return nv ;
    }
}

/*
 * (c) Copyright 2005, 2006, 2007, 2008, 2009 Hewlett-Packard Development Company, LP
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */